The present invention relates to an apparatus and a method for injecting liquid into a container which is entirely sealed except for an injection port. Also, the invention relates to an apparatus and a method for efficiently injecting electrolyte through an inlet in a top cover after the top cover has been attached to a battery case where a battery element is accommodated. In particular, the invention relates to an apparatus and a method for injecting electrolyte suitable for the injection of electrolyte into a nonaqueous electrolyte battery such as a lithium ion battery.
In various fields of industrial and other applications, it is generally practiced to inject liquid into a container which is entirely sealed except for an injection port. For instance, in a lithium ion battery used as a power source for small size electronic devices, active components are coated on a positive electrode current collector and a negative electrode current collector to prepare a positive electrode and a negative electrode respectively. These electrodes are put together with a separator interposed between them and these are wound up to form a battery element. After the battery element is accommodated in a battery case, the battery case is entirely sealed except for an injection port for electrolyte, and then, the electrolyte is injected through the injection port.
FIG. 7 shows the drawings to explain injection process in the assembling procedure of a battery.
As shown in FIG. 7(A), a battery element is accommodated in a battery case 51. A top cover 54 is mounted on the top opening of the battery case 51 by means, such as laser welding, and this top cover comprises a electrolyte injection port 52, an external electrode leading terminal 53, and a pressure relief valve for preventing rupture of the battery when pressure inside the battery is increased. Then, as shown in FIG. 7(B), an injection nozzle 56 of an electrolyte injection apparatus 55 is airtightly mounted on the electrolyte injection port 52 on the top cover 54. An exhaust valve 58 is opened by operating exhaust means 57 of the electrolyte injection apparatus 55, and the air inside the battery case is withdrawn to produce a predetermined degree of reduced pressure. A predetermined quantity of electrolyte 60 is injected into an electrolyte pot 62 via an electrolyte feeding valve 61 from the electrolyte feeding means 59. After the predetermined quantity of electrolyte has been injected, the electrolyte feeding valve 61 is closed.
Next, as shown in FIG. 7(C), the exhaust valve 58 is closed and an electrolyte injection valve 63 is opened. Then, the electrolyte in the electrolyte pot 62 is injected into the battery case due to pressure difference between the air pressure in the battery case and the atmospheric pressure applied on a vent hole 64 on the electrolyte pot. After the electrolyte has been injected into the battery case, a metal piece is attached on the electrolyte injection port, and the injection port is sealed by welding.
The battery element to be accommodated in the battery case is produced as follows: In case of a lithium ion secondary battery, a negative electrode material made of carbonaceous material, on which lithium can be doped or undoped, is coated on a current collector, and a negative electrode is prepared. A positive electrode material of lithium transition metal composite oxide such as lithium cobaltate, lithium manganate, etc. is coated on a band-like current collector, and a positive electrode is prepared. These negative and positive electrodes are bound together with a separator interposed between them and this is wound up, and a battery element is prepared.
In the battery case where the battery element is accommodated, there are a great number of small voids. Even when the air inside the battery case is withdrawn, it takes long time to completely withdraw the air from these small voids. Also, much time is required until the injected nonaqueous electrolyte permeates into the battery element, and it is difficult to inject the electrolyte within short time. The predetermined quantity of electrolyte must be injected to each individual battery. For the purpose of achieving mass production of the battery, it is necessary to arrange many injection apparatuses.
JP-A-07099050 proposes the following apparatus: A battery where electrolyte is to be injected is placed in a chamber. After a predetermined quantity of electrolyte has been filled in a battery liquid pool mounted on the injection nozzle, pressure inside the chamber is reduced, and after removing gas such as the air in the electrolyte or the battery element, the pressure is restored to the atmospheric pressure. Then, pressure is applied further to inject the electrolyte.
In this apparatus, the battery, into which electrolyte is to be injected, is assembled before the top cover is mounted on the top opening of the battery case. In this respect, this cannot be applied to the case where an electrolyte with high viscosity is injected through a small electrolyte injection port of less than 1 mm in diameter as in the case of a small rectangular battery.
It is an object of the present invention to provide an apparatus for injecting liquid into a container, which is entirely sealed except an injection port. In particular, it is an object of the invention to provide an apparatus for injecting electrolyte through an electrolyte injection port into a battery case of nonaqueous electrolyte battery such as lithium ion battery. Also, it is an object of the present invention to provide an apparatus and a method for injecting liquid into many batteries at the same time.
The above objects can be attained by a liquid injection apparatus for injecting liquid into a container, comprising an injection chamber, a container for a liquid to be injected and entirely sealed except an injection port is placed in the injection chamber with the injection port directed downwardly toward the bottom, an injection cell comprising at least one unit injection cell to accommodate the liquid to be injected is installed in the injection chamber, there is provided pressure regulating means to reduce the pressure in the injection chamber and to regulate pressure in the injection chamber to the atmospheric pressure or to a level higher than the atmospheric pressure, the pressure in the injection chamber is reduced to a level lower than the atmospheric pressure by the pressure regulating means at least once, and then, by maintaining the atmospheric pressure or pressure higher than the atmospheric pressure, the liquid is injected through the injection port.
Further, the present invention provides an apparatus for injecting liquid as described above, wherein the unit injection cell is provided with a recess to receive a projected portion of the container when the container is placed in the unit injection cell with the injection port of the container directed to the bottom.
Also, the present invention provides an apparatus for injecting liquid as described above, wherein a member to form a bottom surface of the unit injection cell and a member to form a side wall surface are connected with each other at a curved junction.
Further, the present invention provides an apparatus for injecting liquid as described above, wherein the liquid
Also, the present invention provides a method for injecting liquid into a container, comprising the steps of placing at least one container entirely sealed, except for an injection port, in a unit injection cell of an injection chamber with the liquid to be injected therein, disposing said container in the unit injection cell with the injection port directed to the bottom, reducing pressure in the injection chamber to a predetermined level of pressure, performing at least once an operation to maintain the atmospheric pressure or pressure in the injection chamber higher than the atmospheric pressure for a predetermined period of time and injecting the liquid, and taking out the container to be injected from the unit injection cell.
Further, the present invention provides the method for injecting liquid as described above, wherein said method is a method for injecting electrolyte for a battery.